46 LINNiEAN GENERA. 



eating them. The true nature of this poison has not yet 

 been satisfactorily determined. 



Plate II. fig. 4 and 6. a The cartilage, v v length of the shell, u u 

 breadth of the shell, o disk, r r the beak. 



Mytilus incurvatus — The Incurvated Mytilus. Plate 

 VII. fig. 16. Oblong oval, nearly smooth, both valves much 

 inflated, and curved on one side near the ligament, apex 

 acute, and base much widened. Inhabits the British coasts. 

 Probably it is only a variety of the Mytilus edulis. 



It is to the Mytilus margaritiferus, (the Meleagrina margaritifera of 

 Lamarck,) Plate X. fig. 10, that we are indebted for that precious gem, 

 the oriental pearl. It is an inhabitant of the Indian Ocean ; where it 

 is regularly fished for by men who dive to the bottom of the sea, in 

 places where it frequents. In this perilous employment the divers are 

 often attacked by sharks, and not unfrequently lose their lives.— 

 Mother-of-pearl ornaments are made from the shell itself. 



The Mytili inhabit the ocean, lakes, rivers, and ponds. Marine 

 muscles adhere to rocks or beds by a thin but vei-y tenacious byssus, 

 consisting of extremely fine and tough filaments, and some to the 

 GurgoniiB by a kind of claws. Some penetrate calcareous and argil- 

 laceous rocks, where they reside without changing place, others adhere 

 to rocks or clay on the shore. They are much used for bait or food, 

 and as such they are esteemed by many. The fresh-water muscles are 

 generally found on the surface, or a little way under the mud. Most 

 species of muscles produce peai-ls. 



Genus 17— PINNA. 



Animal a Limax; shell sub-bivalve, fragile, upright, gaping 

 at one end, and furnished with a silky byssus or beard: hinge 

 without teeth. 



Pinna pectinata The Pectinated Pinna. Plate VII. 



fig. 17. Thin, pellucid, light horn coloured ; longitudinally 

 ribbed, and spinous for half its width, obliquely striated, 

 transversely on the other half. Six and a half inches long 

 and three broad. Inhabits the British seas. 



The Pinnjfi, wliich frequently grow to a large size, only inhabit the 

 ocean. They are generally found standing erect in the smoother water 

 bays, mth the broad end or base of the shell uppermost. They are 

 sometimes afiixed by their byssus or beard, to rocks or other bodies, 

 and so firmly attached, that they can by no means be disengaged but 

 at the will of the animal. 



In Italy, the byssus of the Pinna is woven into a sort of silk. The 



